The present invention relates to magnetic materials, and more specifically, to magnetic materials for miniaturized power converters.
The technologies for power conversion devices are transitioning from on-board collections of discrete components to compactly packaged collections of power conversion components on increasingly smaller scales. However, the miniature compact packages may need to be supplemented with additional discrete inductive components.
On-chip inductive components include high energy density materials, such as magnetic materials. Ferrite-based materials and metallic alloys are examples of magnetic materials. Such materials can have thicknesses ranging from hundreds of nanometers (nm) to a few microns. However, ferrite materials are generally processed at high temperatures (e.g., higher than 800° C.), which are not compatible with complementary metal-oxide semiconductor (CMOS) chip wiring processing temperatures. NiFe, CoFe, and CoZrTa are examples of magnetic alloys.
Magnetic metals can be deposited by vacuum deposition technologies (e.g., sputtering), electro deposition, and electroless deposition in aqueous solutions. Vacuum deposition methods can be used to deposit a large variety of magnetic materials. Electrodeposition is used for the deposition of thick metal films because of its high deposition rate, conformal coverage, and low cost. Vacuum methods, however, can suffer from low deposition rates, poor conformal coverage, and the derived magnetic films are difficult to pattern.
Compared to ferrite materials, magnetic alloys can have higher permeability and magnetic flux density, which are necessary to achieve high energy density for on-chip devices. However, the resistivity of magnetic alloys can be low (e.g., less than 50 micro-ohm (μΩ)·centimeters (cm)). Further, because many on-chip devices are operated at high frequencies (e.g., higher than 10 megahertz (MHz)), large eddy currents can be induced within magnetic core. Eddy currents are circular electric currents induced within conductors by a changing magnetic field and result high AC losses at high frequencies. One method to reduce eddy currents is to increase the resistivity of the soft magnetic material so that the eddy currents are confined within each individual magnetic layer. Also thinner magnetic layers have a larger effective magnetic resistance, which results in smaller eddy currents.